The external keratin tissue, which represents the protective covering of the human body, encompasses hair, skin and nails. It is well known that cosmetic treatments alter the character of keratin, and in particular, bleaching, straightening, toning, tinting and permanent waving of the hair exhibit the strongest influence on keratin proteins. Mechanical actions such as combing, brushing and the use of curling irons may also alter the character of hair keratin. Bleaching and tinting, both of which are oxidative chemical processes, convert a substantial amount of cystine, a sulfur containing amino acid, which is a component of keratin, to various oxidative products, cysteic acid being the most prominent moiety produced. In a conventional two step permanent waving process the disulfide bond of cystine is first reduced to two sulfhydryl groups, the cystine being converted to two cysteine moieties. In the second step the sulfhydryl groups are oxidized to convert the sulfhydryl groups back to the cystine disulfide bond.
However, this oxidation reaction generally does not completely convert the sulfhydryl groups back to the cystine disulfide bond. Instead, many of the sulfhydryl groups are oxidized to produce anionic SO.sub.3.sup..crclbar. groups which are present in cysteic acid. Since the disulfide bonds contribute to the strength of hair, hair treated by permanent waving and other cosmetic treatments exhibits a loss of strength of the hair.
Keratinous tissues are normally acidic, having isoelectric points on the acid side of the pH scale. The combination of the normal acidity of hair and the acidic end groups resulting from oxidative cosmetic chemical processes decreases the isoelectric point of hair and makes it even more acidic.
Therefore, hair treated by bleaching, tinting, or permanent waving exhibits a loss of disulfide bonds and increased acidity which are manifested by a loss of the hair's inherent strength and manageability. Thus hair subjected to cosmetic treatment often is in need of additives to restore the hair to its natural qualities and to improve the damaged condition of the hair.
A well known method used to improve the cosmetic feel and appearance of various keratinous materials, especially damaged human hair, skin and nails, is to treat the hair with compositions containing polypeptides. Polypeptides have proven to be especially useful in improving the cosmetic feel and appearance of hair damaged by bleaching processes, tinting and permanent waving.
Polypeptides can be produced by subjecting naturally occurring proteins to acid, base and/or enzymatic hydrolysis. For example, U.S. Pat. No. 3,683,939 describes compositions for treating hair where the compositions contain polypeptides of molecular weight of from 500 to 1500 prepared by partially hydrolyzing collagen by the application of heat and pressure, recovering anions from the formed protein hydrolysate, and completing the hydrolysis with a proteolytic enzyme.
A problem with these compositions prepared by conventional acid, base, and enzymatic hydrolysis methods is that they lack uniformity and consistency for two reasons. First, the quality of the product polypeptides is dependent upon minor variations in such variables as the source of the collagen, the pressure, pH, and length of time of the hydrolysis, and the choice of enzyme for the enzymatic hydrolysis. Second, it is impossible to control which peptide linkages of the collagen are hydrolyzed during the preparation of the polypeptides. Thus different production batches of these polypeptides have different end groups with different chemical characteristics and therefore affect hair differently. Also, these polypeptides generally lack the positive charge necessary to combine with the acidic end groups of hair which have been produced by the more radical salon treatments.
Therefore, it is desirable to produce cosmetic compositions for keratinous tissue containing reproducible polypeptides which are beneficial to the cosmetic appeal, manageability, body and sheen of damaged keratinous tissues. These polypeptides should be derived from proteins so that the positive charges of proteins would be available to neutralize the acidity of damaged hair. Also, these polypeptides should have positive groups located at the extremities of the molecule so that they would be capable of forming ionic bridges between keratin protein chains. In addition, the polypeptides should be of an optimal molecular size to make penetration into the hair shaft possible, and they should be able to be economically manufactured by reproducible means.